Sleeping in at the weekend may be driving obesity and illness, a major study has shown.

Researchers have discovered that the body clock becomes confused by changing sleep patterns when people are not at work, which they have termed ‘social jet lag.’

A study of more than 800 people found that those with a greater difference in sleep between free days and work days are more likely to be obese and suffer from obesity-related disease, than those with little to no difference between these timings.

Unlike travel jet lag, which can cause temporary problems with metabolism, social jet lag can occur chronically throughout an individual’s working life so is more likely to induce more serious and ongoing consequences for the metabolism.

"Social jet lag is an under researched but potentially key contributor to why ‘living against our internal clock’ has an impact on our health," said Dr Michael Parsons, lead author of the study, from the Mammalian Genetics Unit at Medical Research Council.

“Our research confirms findings from a previous study that connected people with more severe social jet lag to increases in self-reported body mass index (BMI), but this is the first study to suggest this difference in sleeping times can also increase the risk for obesity-related disease.”

The study assessed the height, weight and waist circumference of participants in the clinic, as well as measuring biomarkers for inflammation and diabetes in the blood.

It then compared these findings with results from a questionnaire which assessed participants sleep duration and chronotype - their preference in sleep timing.

The researchers found that just a two hour difference in sleep patterns at the weekend can increase the risk of an elevated BMI and biomarkers for inflammation and diabetes.

The reasons for these increases are unknown, but a possibility is that social jet lag disrupts healthy habits such as diet and exercise in a way that may compromise health.

Dr Terrie Moffitt, co-author of the paper, added: “These findings help us start to actually understand the physiology of social jetlag and how it impacts upon obesity and obesity-related disease.

“Further research that determines this association could help inform obesity prevention by influencing policies and practices that contribute to social jetlag, such as work schedules and daylight savings.”

Professor David Lomas, Population and Systems Medicine Board Chair at the Medical Research Council, said: “This study adds further evidence to previous research that living against our body clock, even if just on a small scale, may be part of the problem behind rising obesity and related disease.

“It could allow for exploration of how changes to our diary as well as diet, could help to reduce this upwards trend and improve public health.”